The present invention relates to a drill insert to be engaged with a rotary cutting tool for drill working operation use.
An outer edge insert and an inner edge insert engaged with the tip end portion of the tool main body for free detachable operation has been used as a drill tool for effecting a hole working operation so that the mutual rotation tracks may be crossed.
FIG. 4 shows an arrangement where two conventional drill inserts 10 to be used in a drill tool are engaged with a drill tool main body T.
The drill insert 10 has a top face 11 defining a pointed angle portion, a polygon plate-shaped body, cutting edges formed in the pointed angle portion of the top face 11. As shown in FIG. 4, two are engaged in one drill tool main body T respectively as the outer edge insert 12 and the inner edge insert 13 with the top faces 11, 11 being directed in the same rotating direction. Also, the rotating track of the cutting edge which becomes the bottom cutting edge 15 among the cutting edges formed in the outer edge insert 12 and the inner edge insert 13 is mutually crossed to cover from the central shaft T1 to the side face T2 of the tool main body T.
In FIG. 4 (b), a composition force N of the load force in a radial direction to be caused respectively in the outer edge insert 12 and the inner edge insert 13 is shown when the cutting working operation has been effected by a drill tool engaged with the drill insert 10. As shown in FIG. 4, in the conventional drill insert 10, the radial direction load to be applied upon the inner edge insert 13 is caused along the bottom cutting edge 15 of the inner edge insert 13 from the central shaft T1, while the outer edge insert 12 causes in the reverse rotating direction (direction of +), with a radius for connecting the corner R portion 14 with the central shaft T1 or the tool main body T as a reference, by the cutting resistance the corner R portion 14 for cutting the outer wall receives.
As a result, the composition force N of the load force in the radial direction is directed onto the side of the inner edge insert 13, namely, it is bent in a direction along which the hole diameter may become smaller during the working operation. In pulling out the drill tool from the work, the outer edge insert 12 comes into contact with the hole wall to damage the finish face. When the pulling is effected with a quick-acting operation, the corner R portion 14 of the outer edge insert 12 hits strongly the wall. On the other hand, in the pulling operation during the cutting feeding, the contact frequency increases to give larger damages to the corner R portion 14 of the outer edge insert 12.
Accordingly, an object of the present invention to provide a drill tool capable of working into better finish face without contacting between the outer edge insert and the hole wall in pulling of the drill tool from the work.
In a drill insert of the present invention where cutting edges are formed on the top face pointed angle portion of a polygon plate-shaped body, a pair of cutting edges in a symmetrical relation mutually with respect to the central shaft of the insert are formed as major cutting edges, a projection portion having a corner R portion continuous to the major cutting edge and a corner R portion opposite mutually with respect to the corner R portion is provided respectively on a pair of cutting edges continuous to the major cutting edge and in a symmetrical relation to each other with respect to the central shaft of the insert.
The drill insert of the present invention has a projection formed having a pair of corner R portions formed in each of a pair of cutting edges continuous to the major cutting edge, among the cutting edges formed on the top face pointed angle portion, and having a symmetric relation as described above. As these corner R portions are arranged on the hole bottom side of the outer edge insert so that the radial load of the outer edge insert is directed onto the side of the rotating direction (direction of -), thus directing onto the outer edge insert side from the central shaft.
Accordingly, the tool main body is bent onto the side of the outer edge insert so that the drill tool can be pulled from the work without contacting between the outer edge insert and the hole wall.
Also, as another function of the drill insert of the present invention, the corner R portion, from the corner R portions for constituting the projecting portion of the outer edge insert opposite onto the hole bottom side, which is not continuous to the major cutting edge, severs the chips from the hole bottom side so that the chips on the side of the outer edge insert side are severed smaller and are discharged.